I find myself from time to time stumbling across networks and companies that fail to keep their applications and servers up to date. This is a big no-no as it makes you an easy target for hackers.
By not updating you are leaving gaping KNOWN holes in your systems. Make sure everything is up to date. On the flip side make sure all those updates, hotfixes and service packs are tested before deploying them company wide!
How do you keep your network up to date?